Abstract: Kidney stone disease (KSD) causes significant morbidity and financial burden on public health. The lifetime prevalence of KSD is increasing, with data from the most recent National Health and Nutrition Examination Survey (NHANES; 2007?2010) reporting an 8.8% population prevalence-a substantial increase from the 5.2% prevalence reported in a prior NHANES cohort . The rising prevalence of obesity and diabetes, two well established risk factors for KSD, together with population growth is projected to contribute an additional $1.24 billion/year in US treatment costs by 2030 2. In addition to obesity and diabetes a variety of systemic diseases, such as the metabolic syndrome, hypertension, chronic kidney disease (CKD) and cardiovascular disease are associated with KSD. Based on current thinking that pathological changes in metabolism play a key role in development of kidney stones; diet, as a primary determinant of an organism?s metabolism, is generally believed to be an important contributing factor to KSD. Recent evidence strongly suggests that the gut microbiome (GMB) is a modulating factor of diet-driven metabolism. Whilst acknowledging that diet (and its effect on metabolism) is an important factor in the pathogenesis of KSD, the overarching hypothesis to be tested in this proposal is that the gut microbiome (GMB) can influence the metabolic effects of diet resulting in KSD. Our preliminary data supports this hypothesis and motivates us to test the following two hypotheses in this proposal: 1) In Specific Aim 1 we will test the hypothesis that a distinct GMB is associated with KSD patients and non-stone formers (controls). Using the latest innovations in the extraction, amplification and next-gen sequencing of fecal flora, we will explore differences in the GMB between KSD patients and non-stone formers (controls). 2) In Specific Aim 2 we will test the hypothesis that while the GMB in kidney stone patients is a dynamic entity with day-to-day compositional variation, it will over time maintain a stable enterotype partition despite dietary modification. We will assess the variability of the GMB profile (both within and between patients) at various time points following adoption of dietary interventions in kidney stone patients. If our hypothesis is proven correct it could form the basis of a GMB screen to identify patients at risk of KSD and also support a strategy for treatment and prevention of KSD through modulation of an individual?s GMB.